PORTLAND, Maine — A lawsuit filed on behalf of two southern Maine residents on Tuesday asks a federal judge to intervene to step up the state’s timetable for redistricting to ensure it’s completed in time for next year’s congressional elections.

Maine law requires congressional redistricting to be done in 2013. The lawsuit contends there’s no good reason to wait until then because the 2010 Census data already are available.

“Most states, when they get these numbers, they redraw the lines before the next imminent election,” said Timothy Woodcock, who filed the complaint in U.S. District Court in Bangor.

Maine and Montana are the only states that allow redistricting to wait until after the 2012 congressional elections, said Tim Storey, a redistricting expert with the National Conference of State Legislatures. Four states are scrambling to use Census data to redistrict for legislative races later this year.

The Maine Constitution requires redistricting for state House and Senate races in 2013. By state law, congressional redistricting uses the same dates.

The federal complaint contends the new census data point to a population shift that means there’ll be 8,669 more residents in the southern 1st Congressional District than in the 2nd Congressional District, a disparity that must be corrected before congressional elections next year.

The census showed the 1st District had 668,515 residents while the 2nd District had 659,846.

If the disparity isn’t corrected, the vote of people in the more heavily populated southern district will be diluted, a problem that runs afoul of the U.S. Constitution, Woodcock said.

The complaint asks the federal court to assume jurisdiction over Maine’s redistricting process and require that the lines be redrawn this year instead of in 2013, so the districts’ populations are basically equal before the election.

“Once we have the Census data, there isn’t really a good public policy reason not to incorporate that Census data if it’s logistically possible in time for the next congressional election,” Woodcock said from his Bangor office. “The state should be compelled to do that.”

Storey, the redistricting expert, said he’s surprised a lawsuit challenging Maine’s redistricting wasn’t filed a decade ago. The “one-person, one-vote” standard set forth by the Constitution sets a high threshold that could make it difficult to defend Maine’s existing system, he said.